Forget unstructured data "In other words, all data is structured - it is just that some data is more structured than others. Actually, our misconceptions go further than this. The truth is that a photograph has more structure than a sales order, say. In fact, it has so much structure that we cannot usefully encapsulate it.
Indeed, this has important consequences for the way we that we think about metadata. This usually described as data about data. Now, consider the metadata that you would require to describe the Mona Lisa. We could agree that it was a painting, a portrait of a woman, and that it was painted by Leonardo. But metadata is supposed to describe the data: could you get any two people to agree on how to describe the Mona Lisa? And, if you can't get agreement on your metadata then it ceases to be worthwhile.
Perhaps then that is the distinction we need: it is not a question of whether data is structured or not, but actually about whether the data can be fully described by the relevant metadata."